printf() and scanf() Functions in C

In C programming, printf() and scanf() are the most commonly used functions for performing input and output (I/O) operations. These functions are part of the Standard Input/Output Library (stdio.h), which needs to be included in your program to use them.

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1. printf() Function

The printf() function is used to output (print) data to the standard output device, typically the console.

Syntax:

printf(format_string, argument_list);

• format_string: A string containing text and format specifiers.
• argument_list: Values to be printed that correspond to the format specifiers.

Common Format Specifiers:

Specifier	Meaning
%d	Integer
%f	Floating-point number
%c	Single character
%s	String (sequence of characters)
%lf	Double-precision floating-point
%x, %X	Hexadecimal integer
%o	Octal integer

Example:

#include <stdio.h>

int main() {
    int students = 100;
    float pass_percentage = 75.5;
    char grade = 'A';
    char founder[] = "Pawan Jaiswal";

    printf("Number of students: %d\n", students);  
// Integer output
    printf("Pass percentage: %.2f%%\n", pass_percentage);  
// Float with two decimal places
    printf("Grade: %c\n", grade);  
// Character output
    printf("Founder: %s\n", founder);  
// String output

    return 0;
}

Output:

Number of students: 100
Pass percentage: 75.50%
Grade: A
Founder: Pawan Jaiswal

Explanation:

• %d: Prints an integer.
• %.2f: Prints a floating-point number with 2 decimal places.
• %c: Prints a single character.
• %s: Prints a string.

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2. scanf() Function

The scanf() function is used to get input from the user and store it in variables.

Syntax:

scanf(format_string, &variable_list);

• format_string: A string containing format specifiers.
• variable_list: The addresses of the variables where the input will be stored.

Common Format Specifiers:

Specifier	Meaning
%d	Integer
%f	Floating-point number
%c	Single character
%s	String (no need to use & with strings)
%lf	Double-precision floating-point

Example:

#include <stdio.h>

int main() {
    int students;
    float pass_percentage;
    char grade;
    char founder[50];

// Input for integer, float, character, and string
    printf("Enter the number of students: ");
    scanf("%d", &students);  
// Integer input

    printf("Enter the pass percentage: ");
    scanf("%f", &pass_percentage);  
// Float input

    printf("Enter the grade: ");
    scanf(" %c", &grade);  

// Character input (note the space before %c)

    printf("Enter the founder's name: ");
    scanf("%s", founder);  

// String input (no & needed for string)
// Output the values entered

    printf("Number of students: %d\n", students);
    printf("Pass percentage: %.2f\n", pass_percentage);
    printf("Grade: %c\n", grade);
    printf("Founder: %s\n", founder);

    return 0;
}

Output (Example of user input):

Enter the number of students: 100
Enter the pass percentage: 85.75
Enter the grade: A
Enter the founder's name: Pawan

Number of students: 100
Pass percentage: 85.75
Grade: A
Founder: Pawan

Explanation:

• %d: Reads an integer.
• %f: Reads a floating-point number.
• %c: Reads a single character (space before %c is used to ignore any newline left in the buffer).
• %s: Reads a string (does not require the & operator).

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Important Points About printf() and scanf()

1. Format Specifiers:
   • Make sure the format specifier matches the type of variable you are using, or the output/input may be incorrect.
   • Example: Use %d for integers, %f for floats, %s for strings, etc.
2. Reading Input:
   • scanf() requires the address of the variable using the & operator, except for strings.
   • Always leave a space before %c in scanf() when reading a character after other inputs to handle newline characters left in the buffer.
3. Handling Strings:
   • In scanf(), string input stops at the first whitespace character (space, tab, or newline).
   • To read multi-word strings, use gets() (deprecated) or fgets().
4. Floating-Point Precision:
   • You can control the number of decimal places displayed using %.nf in printf() where n is the number of decimal places.
5. Escape Sequences:
   • Use escape sequences in printf() to format the output:
     • \n: Newline
     • \t: Tab
     • \\: Backslash
     • %%: Prints a percent sign

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Advanced Example Using printf() and scanf()

#include <stdio.h>

int main() {
    int employees;
    float revenue;
    char grade;
    char company_name[50] = "SamagraCS Educational Technology";
    char founder_name[30];

    // Input section
    printf("Enter the number of employees: ");
    scanf("%d", &employees);

    printf("Enter the revenue in millions: ");
    scanf("%f", &revenue);

    printf("Enter the grade of the company: ");
    scanf(" %c", &grade);  // Note the space before %c

    printf("Enter the founder's name: ");
    scanf("%s", founder_name);

    // Output section
    printf("\nCompany Name: %s\n", company_name);
    printf("Number of employees: %d\n", employees);
    printf("Revenue: $%.2f million\n", revenue);
    printf("Company Grade: %c\n", grade);
    printf("Founder: %s\n", founder_name);

    return 0;
}

Output:

Enter the number of employees: 150
Enter the revenue in millions: 12.75
Enter the grade of the company: A
Enter the founder's name: Pawan Jaiswal

Company Name: SamagraCS Educational Technology
Number of employees: 150
Revenue: $12.75 million
Company Grade: A
Founder: Pawan Jaiswal

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